The following descriptions and examples are not admitted to be prior art by virtue of their inclusion within this section.
Wavelength Division Multiplex (WDM) systems use lasers as optical sources for transmitting information. Optical channels may be multiplexed using wavelength division multiplexing, thereby allowing approximately simultaneous transmission of multiple channels of data along an optical fiber. Each optical channel may correspond to an optical wavelength.
There are several types of lasers, including gas lasers, solid-state lasers, liquid (dye) lasers, free electron, and semiconductor lasers. Lasers generally have a laser cavity defined by an optical gain medium in the laser cavity and a method for providing optical feedback. The gain medium amplifies electromagnetic waves (light) in the cavity by stimulated emission, thereby providing optical gain.
In semiconductor lasers, a semiconductor active region serves as the gain medium. Semiconductor lasers may be diode (bipolar) lasers or non-diode, unipolar lasers such as quantum cascade (QC) lasers. Semiconductor lasers are used for a variety of industrial and scientific applications and can be built with a variety of structures and semiconductor materials.
The use of semiconductor lasers for forming a source of optical energy is attractive for a number of reasons. Semiconductor lasers have a relatively small volume and consume a small amount of power as compared to conventional laser devices. Further, semiconductor lasers can be fabricated as monolithic devices, which do not require a combination of a resonant cavity with external mirrors and other structures to generate a coherent output laser beam. For monolithic designs, the optical feedback is typically provided by a reflector or reflectors external and/or adjacent to the optical gain medium or some combination of feedback mechanisms. For example, in Fabry-Perot or Vertical-Cavity Surface-Emitting Laser (VCSEL) lasers a set of mirrors or cleaved facets that bound the optical gain medium may provide the optical feedback. In distributed feedback (DFB) lasers, a distributed reflector along the gain medium may provide the feedback. The distributed reflector may be a Bragg reflector (i.e., Bragg grating). A distributed Bragg reflector (grating) may also be used as an external reflector. In this case, a Bragg grating or gratings may be at or near the ends of the gain medium. A laser with a distributed Bragg reflector as an external reflector is known as a Distributed Bragg Reflector (DBR) laser.
Semiconductor lasers may be configured to emit optical energy at one wavelength or more than one wavelength. A semiconductor laser that is configured to emit optical energy at more than one wavelength may be tunable. In a tunable laser, an emission wavelength may depend on one or more operational parameters.
The particular operational parameters may be laser dependent. A value or a range of values of the operational parameters may be determined when the laser is initially tested and calibrated. It may be desirable to provide the operational parameters in a convenient format for an end-user. This may include providing tables of these parameters in a storage medium such as a removable computer readable disk. Because such a disk may be misplaced, it may be desirable to provide these parameters integrated with a laser package.